7 Years
The last "7 years" of Daniel 9, that ends with the return of Christ (see Mt. 24:15,21,29), starts off with a 7-year covenant, or "peace deal," that includes allowing the Jews to rebuild their temple of worship. (Something to keep an eye out for.) In the middle of the 7 years the "peace deal" will be broken by the "Antichrist" (AC) which will begin the 3.5-year period of "Great Tribulation" where the AC will set up the "Abomination of Desolations" in the Jewish temple, demand people worship him as God, and actively persecutes and in some cases kills Christians and all those who don't take the "Mark of the Beast." (See Revelation 13)
At the end of the 3.5 years of "Great Tribulation" (GT) Christ returns to "Rapture" (take home to Heaven) His saints. (See also 1Thes 4:13-17; 2Thes 2:1-4) Then begins the 75-day period of the "Wrath of God" taking place on Earth, while during the first 30 of those days the Saints are in Heaven at the "Marriage Supper of the Lamb". Shortly after the start of the 75-day period of wrath, Babylon the Whore (the epitome of which is arguably the USA) is destroyed in what appears to be a nuclear attack. After the first 30 of those 75 days are up, Christ and His saints return to the Earth for the "Battle of Armageddon" where they fight and destroy the AC and his armies, after which Satan is bound and cast into the bottomless pit.
Note that there are several approaches to the timing of the Great Tribulation, the Rapture, and the Wrath, which I won't go into detail over. Just to briefly mention a few here, there is the Rapture before, in the middle, and at the end of the Great Tribulation. There are also different views about how long the Saints will be in the GT, whether the 7 trumpets are during the GT or wrath, and how long the period of wrath lasts. There's even a view that seems to suggest that the verses in Daniel are not related to those in Revelation. I'll try to post a few links in the footer section of some of these views.
Points to consider: There is a sometimes-overlooked correlation between the beasts in Daniel and Revelation. In Daniel 7 there is the beast like a bear with one side higher than the other representing the Medo-Persian empire. The 3 ribs in his mouth represent the former world powers of Egypt, Assyria and Babylon. Next the beast like a leopard representing Greece with four heads and four wings. And the last beast representing Rome being diverse from all the rest. It's described as dreadful and terrible and strong exceedingly with teeth of iron.
The 10 horns on the last beast represent 10 future kingdoms that are somehow connected to Rome, most likely 10 European nations. Among the 10 horns comes up a little horn that plucks up 3 of the 10 horns. The little horn and the 10 other horns in the end work together in unison to form the final world power (probably Russia and Europe) in the end times. As a whole 7 kingdoms are represented here in Daniel. In Revelation there is the 7 headed dragon (Rev. 12:3) and the 7 headed beast (Rev. 13:1-2; 17:3,7-18) both with 10 horns. The 7 headed dragon is depicted as Satan, the spirit behind the 7 dominant kingdoms of world history represented in both visions as the 7 heads.
Here in Revelation the Beast of chapter 13 is the last world power in the end times with allusions in this vision to the lion, bear, leopard and 10 horned beasts in Dan. 7. Another correlation between Daniel and Revelation is the 3.5 years associated with the GT. There are several references to this that are expressed in several ways, 42 months (Revelation 11:2; 13:5), 1260 days (Revelation 11:3; 12:6), a time and times and half a time (Daniel 7:25; 12:7; Revelation 12:14), and midst of the week (Daniel 9:27).
Another consideration has to do with the "servants of our God" being sealed in their foreheads in Rev. 7:3. Rev. 9:4 indicate this "sealing" is for some kind of special protection from God. At face value "servants of our God" in this context would refer to followers of Christ. Looking at the rest of the chapter 144,000 "followers of Christ" of the tribes of Israel are sealed. Then it goes on to a vision of a multitude that no man could number that went through the GT. So altogether there are an innumerable multitude of "servants of our God" that are sealed in their foreheads that receive special protection from God during the GT.
Some argue that the "servants of our God" get sealed for the wrath period. It seems to make more sense that this is talking about the GT as there are passages that indicate that the Church will go through the 3.5 years of GT such as Revelation 12:6 and 14, not to mention Mt. 24:15, 21,29. Again this would depend on large part if the 7 Seals are interpreted as a general timeline of events or more specifically events of the GT.
I won't go too much into further detail except to say one last thing. When the 7th trumpet sounds it says, "The kingdoms of this world are become the kingdoms of our Lord, and of His Christ." Some would interpret this to be the beginning of the 1000-year reign of Christ. But if you go further on in the passage it states, "And the nations were angry, and thy wrath is come, ..." This, most probably, is in reference to the period of the 7 vials of God's wrath. So it seems verse 15 is talking in general terms relating the 7th trumpet sounding to bringing in Jesus' reign with the Rapture as the starting point.
Footnote: Ezekiel 38-39 gives further insight into the AC and the "Battle of Armageddon". The main noteworthy detail in these passages is that the AC will come from the land of Magog, an ancient name associated with Russia. There are also scriptures that indicate that the AC will come out of a kingdom that has some association with the former Roman empire, of which an argument could be made that Russia would be considered as a contender. (See Daniel 7:23-25, and Revelation 17:10-14)